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ENVB 210 > Biosphere V > Flashcards

Biosphere V Flashcards

1
Q

How does the presence of water solubility affect the speed of decay?

A

It increases the speed of decay because it gets broken down into smaller components more easily.

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2
Q

What is net primary productivity?

A

The carbon that remains in the plant biomass at the end of the growing season (not including CO2 respired by the plant (gross productivity).

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3
Q

What is the relationship between NPP and SOC?

A

Regions with high primary productivity will tend to have high SOC as well.

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4
Q

What regions have a high NPP and SOC?

A

The northern latitudes and the tropics.

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5
Q

Why is there are lot of SOC in the tropics?

A

There’s no end to the growing season, so there’s a constant cycle of deaths and nutrients.

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6
Q

Why is there a lot of SOC in the north?

A

Climate change is going to cause permafrost melt, meaning that the microbial communities in frozen environments is becoming active. Normally, the soil OM stays as OM, but once the permafrost melts, they start respiring.

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7
Q

Name 4 steps of decomposition.

A
  1. Mechanical and biological fragmentation, creating soluble sugars, amino acids, and NO3
  2. Further biological fragmentation of soluble sugars, amino acids, and NO3
  3. Extracellular enzymes break it down into complex polymers such as cellulose, lignin, and protein
  4. Extracellular enzymes break polymers down into monomeric units such as sugars, phenols, and amino acids
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8
Q

Name which organisms are responsible for each step of decomposition.

A
  1. Larger organisms (e.g. earthworms)
  2. Smaller organisms like collebola and mites
    3 and 4. Extracellular enzymes of biological origin
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9
Q

What is the fate of monomeric units after decomposition?

A

They enter soil solution and are absorbed into microorganisms’ bodies.

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10
Q

Describe the process by which NPP turns into SOM.

A

The NPP enters the soil and gets enzymatically broken down. Some of the resulting compounds are assimilated into decomposer biomass and others are mineralized into CO2, ammonium, or phosphate. The microbial community synthesizes new cell walls/lipids, nucleic acids. Some of the original plant compounds become physically or chemically protected from further decomposition.

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11
Q

Describe the decomposition curve, including mass of plant little remaining, acucmulation of transformation products, and net mass remaining.

A

Mass of plant litter starts at 100% and goes down to zero over time. Transformation products accumulate from 0 to around 25%. The net mass remaining declines from 100% to 25%.

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12
Q

What are the four types of soil organic matter?

A

Above-ground plant inputs, microfauna, below-ground plant inputs (roots), and macrofauna.

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13
Q

Explain the role of SOM in nutrient provision.

A

It is the major and often only source of macro and micro nutrients.

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14
Q

Explain the role of SOM in transport/availability of metals.

A

Because of its high CEC and its ability to create aggregates, SOM is good at retaining pesticides and metals, reducing pollutants.

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15
Q

Compare the relative sizes of the 3 main soil C stores.

A

Atmospheric: 800 Gt
Plant biomass: 550 Gt
Soil carbon: 2300 Gt

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16
Q

Why is the difference in size between soil stores significant?

A

If you lose 10% of carbon in the soil via respiration in to the atmosphere, this small amount ends up being a large portion of what was already in the atmosphere. So, small losses of soil carbon can have major implications for atmospheric carbon. Also, inputs from plant biomass take a long time to impact the soil carbon.

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17
Q

SOM storage is a function of […] and […]

A

Inputs, outputs

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18
Q

What is the major SOM input and output?

A

Input: plant photosynthesis converting CO2 into organic carbon in plant tissue
Output: microbes and soil animals release CO2 when they eat plant materials.

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19
Q

Describe the balance between SOM inputs and outputs under mature or stable circumstances.

A

Under these circumstances, the inputs and outputs and approximately equal.

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20
Q

Describe the balance between SOM inputs and outputs under disturbance conditions.

A

Under these conditions, there is likely to be an imbalance between inputs and outputs leading either to a net loss of soil organic C or a net gain of organic C.

21
Q

Name 4 factors that affect SOC concentrations?

A

Ecosystem/climate, cover crops, soil texture, soil horizon/depth

22
Q

Describe how crop type can affect soil C inputs in agricultural systems.

A

The harvest index and root:shoot ratio can affect how much carbon ends up entering the soil. A crop with a high harvest index, such as corn, is mostly removed, so little of that carbon enters the soil. A crop with a high root:shoot ratio means that much of its biomass is occupied by roots, which will do a better job of retaining C in the soil .

23
Q

Compare corn and alfalfa in terms of SOC inputs.

A

Corn has a low root:shoot ratio and a high harvest index, so little biomass ends up entering the soil. Alfalfa has a high root:shoot ratio (very deep rooting system), so it will add more C to the soil.

24
Q

Why do grasslands have high amounts of soil C?

A

Because of the extensive root system of grasses.

25
Q

How do root inputs affect C inputs into soil?

A

They are responsible for 30-50% of belowground C and contribute to long term carbon storage.

26
Q

Name 4 reasons why roots promote C accumulation.

A
  1. They are protected within aggregates
  2. They have compounds called rhizodeposits that resist decomposition
  3. Exudates adsorb to soil minerals
  4. They feed microbes, which add to soil C.
27
Q

What carbon fraction(s) does root C contribute to?

A

It contributes to both the fresh C fraction and the stable C fraction. But importantly, it makes up the vast majority of the stable C fraction.

28
Q

What is the relationship between microbial abundance and SOM? Why?

A

There is a direct relationship between microorganism abundance and SOC because microorganisms contribute to SOM through respiration, and also contribute when they die.

29
Q

What are the two categories of SOM?

A

POM = particulate organic matter.
MAOM = mineral-associated organic matter

30
Q

What is the difference POM and MAOM?

A

POM is detritus in various stages of decomposition. MAOM is very decomposed and has been transformed by living organisms.

31
Q

Compare POM and MAOM in terms of:
a) Ease of decomposition
b) Residence time
c) Level of protection
d) Contribution to total SOM.

A

a) POM easily decomposed, MOAM high stable
b) POM RT short, from days to years, MAOM RT long, for hundreds to thousands of years
c) POM highly accessible to soil organisms, MAOM physically protected
d) POM 10-20% of SOM, MAOM 60-90% of SOM

32
Q

Which category of SOM contributes the most to long term sequestion?

A

MAOM

33
Q

Compare how the POM SOC stock compares to the MAOM SOC stock after many years of land use.

A

The POM stock will have lost the vast majority (90%) of its mass, while the MAOM stock will have lost only around 30%. MAOM is way more persistent.

34
Q

Compare how the POM SOC stock compares to the MAOM SOC stock after the management of OM is improved from normal cultivation.

A

There will mainly be an increase in POM, and it is not going to store in the long term fraction (MAOM) for a long term). As time passes, OC will add to MOAM.

35
Q

Name the 3 main mechanisms of carbon storage in order of magnitude of protection from disturbance.

A

Slow decomposition, physical, mineral

36
Q

Explain how slow decomposition works as a mechanism for soil carbon storage.

A

The climate constrains microbial activity, as cold climates and/or lack of oxygen discourage microbial activity. It also can occur depending on the type of litter/litter chemistry, as more lignin will result in slower decomposition.

37
Q

Explain how physical protection works as a mechanism for soil carbon storage?

A

Some soil carbon is made inaccessible to decomposition via aggregation (most common), soil moisture availability, and distance from microbes if deep in soil profile.

38
Q

Explain how mineral works as a mechanism for soil carbon storage.

A

It is based on binding mechanisms between SOM and minerals, such as H bonding, cation bridging, and ligand exchanges

39
Q

How does clay content affect mineral protection of SOC?

A

More clay content = more protection

40
Q

How does clay type affect mineral protection of SOC?

A

2:1 clays will facilitate more mineral protection than 1:1 clays because they have a higher charge and a higher sorption.

41
Q

How does the prevalence of metal oxides affect mineral protection of SOC?

A

More metal oxides, especially Fe and Al, improve SOM bonding.

42
Q

How does the ionic composition of soil affect mineral protection of SOC?

A

High presence of cations = SOM bonding

43
Q

Describe the pattern of organic C stock in Canadian soils.

A

It is most concentrated in the Northeast (above Ontario). This is because most peatlands are there, so there is slow decomposition.

44
Q

What types of ecosystems store the most carbon in the soil?

A

Wetlands, boreal forests, and temperate grasslands

45
Q

How does adding cover crops affect soil (generally)?

A

Generally, adding cover crops increases the carbon inputs into soil.

46
Q

Which soil texture benefits the most from the addition of cover crops for the addition of soil C? Why?

A

Fine (clayey) soil. This is because the soil will be more capable of retaining the carbon and providing mineral protection.

47
Q

Which type of planted crop benefits soil the most in terms of soil C addition with the addition of cover crops?

A

A non-legume

48
Q

Which type of cover crop is most effective in terms of soil C addition?

A

When it is a mixture of grass and legumes.

49
Q

Do surface soils or subsurface soils benefit more from cover crops in terms of soil C addition?

A

Surface soils benefit the most.

ENVB 210 (16 decks)

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